This invention relates generally to the field of printing utilizing ink jet technology, and more particularly to a method of utilizing ink jet technology to print discrete portions of postage indicia images with inks having distinct and unique characteristics.
Postage meters having printing devices for printing postage indicia on envelopes have long been well known and have achieved almost universal acceptance and use in all manner of commercial environments, as well as in limited forms of home use. Typically the postage meter is part of a mailing machine which has the capability of automatically feeding a succession of envelopes from a supply thereof past the postage meter where the printing device prints the postage indicia on the envelope, and then ejecting the envelopes from the mailing machine for further processing, such as stacking for transfer to a postal facility.
The traditional forms of printing devices utilized in postage meters for half a century or more have used metal dies suitably mounted in the printing device to which ink was applied between each printing operation by a suitable inking device. In one form of printing device, the die had a curved surface and was mounted on a rotating drum so that it could print an indicia on an envelope while the envelope was moving through the postage meter. In another form, the die was flat, and the printing operation took place while the forward motion of the envelope was momentarily arrested and the envelope pressed into firm engagement with the die. These forms of printing devices were generally mechanically complex, large and cumbersome and relatively expensive, and due to the relatively permanent nature of the die, any change in the format of the indicia, whether in the graphics or alpha-numeric component of the indicia, required the purchase of a new die, which itself was expensive.
The advent of ink jet technology opened up a new field of printing techniques for printing postage indicia on envelopes, with the result that new types of postage meters could be developed utilizing the ink jet technology in one form or another which would be far less complex, less cumbersome and less costly, and any desired changes in the format of the indicia could be made simply by changing software in the postage meter. Another advantage of this printing technique is that it affords higher resolution print than the conventional impact meter printing techniques. Thus, the new technology, which had become so prevalent in other printing applications, held the promise of dramatically changing the time honored traditional forms of postage meter printing devices.
In the course of development of various forms of ink jet printing devices for use in postage meters, one very significant problem soon became apparent, which was that postage indicia could not be printed with the typical inks developed for use in ink jet printing devices. One significant difference between general printing applications and the printing of postage indicia is that the latter is, in effect, printing money, and therefore appropriate security measures must be taken to ensure that indicia already printed on envelopes cannot be reused.
This problem first arose with the use of postage stamps which were adhesively applied to envelopes to evidence the payment of the fee required for the handling of mail, and the problem was solved by a technique called canceling, which was simply the printing by the Post Office of a particular graphic design, the cancellation mark, on the stamps as evidence that the stamps had been used and could not be used again. This same technique was used in the early development of printing devices for postage meters so that an indicia could not be cut off of one envelope and pasted onto another. In either event, in order for the mail to be properly canceled, it had to be in the same orientation so that it could be fed at high speed through the canceling machines.
As time passed, the Postal Service has substantially discontinued the practice of running mail with postage meter indicia thereon through canceling machines. However, a more significant problem than the security aspect discussed above is that in modern mail handling facilities, where enormous quantities of mail are handled on a daily basis, the mail must be sorted in high speed automatic sorting machines, and this requires that certain information on the front of the envelopes, typically addresses in bar code form and postnet bar codes, be machine readable. Thus, all mail, regardless of whether it bears stamps or printed postage indicia, must be oriented in the same manner, a requirement similar to that for passing the mail through canceling machines.
Thus, regardless of the purpose of orienting the mail in a uniform manner, this is accomplished in so-called automatic facing machines in which a fluorescent material detecting device looks at the postage stamp or postage indicia area of the envelopes passing through the facing machine for the presence of fluorescent material. This material was incorporated into postage stamps and has also been incorporated into the ink used in conventional postage maters, so that if the fluorescent detector in the facing machine does not detect fluorescent material as an envelope passes the detector, the envelope is diverted out of the normal path of the mail and is reoriented and again passed through the facing machine to ensure that it is then properly oriented. This process can be repeated until the facing machine finally detects that the envelope is properly oriented. Without this type of automatic equipment, the drastic reduction in the through put rate in modern mail handling facilities would virtually bring the system to a halt.
As time passed, it became apparent that the ink used in the former die type printing devices, in addition to being fluorescent, also had to be water fast in order to meet rigid Postal Service standards for acceptable postage meter ink. There are many ways in which mail can be subject to excessive moisture, such as water from envelope sealing devices in the mailing machines inadvertently transferring onto the postage indicia, rain reaching the envelopes during outdoor transfer, spilling of liquids in the office, etc. The moisture from any of these or other causes can smear the ink of an indicia after it is printed and render it either unreadable by the human eye or by machine readable techniques. Therefore, inks were developed which had essentially an oil base constituent which was more thoroughly absorbed into the fibers of the paper from which the envelopes were made than water base inks, with the result that they would not smear even from being subjected to excessive moisture, such as the direct application of water.
Thus, the ink generally accepted for use in postage meters for a long period of time had the characteristics both of being highly water fast, i.e., sufficiently permanent so as not to smear even if subjected to excessive moisture, and also fluorescent so as to be machine readable to facilitate proper orientation of the mail in automatic high speed canceling and/or sorting machines.
As briefly noted above, in the course of the development of postage indicia printing devices utilizing ink jet technology, it was soon recognized that the inks developed for use in ink jet printing devices could not be used to print postage indicia because there was no machine readable fluorescent material in those inks. Also, the commercially available inks used in the conventional postage meters could not be used in the most desirable technique for ink jet printing, that of bubble jet printing, because the oil base prevented the ink from boiling and vaporizing in the ink ejecting mechanism to eject ink from the nozzles of the printing device, thereby rendering the commercially available postage meter ink unusable. Thus, it was found that the dye structures of the inks were such that the characteristics of water fastness and fluorescence could not be combined in a single ink that would work in ink jet printers of the bubble jet type, since these printers require water base ink.
It was soon found that the dye structure of the inks being used for printing postage meters was such that the essential characteristics of water fastness and fluorescence simply could not be combined in a single ink that would be suitable for the most desirable technique of ink jet printing, that of bubble jet printing. The constituent of the ink that makes it water fast has an adverse effect on the fluorescence, thereby rendering the indicia unreadable by the known fluorescent detectors, and eliminating that constituent prevented the ink from being water fast.
Thus, the entire development of a commercially acceptable ink jet printing device for use in postage meters was seriously impeded for lack of a readily available and commercially viable ink. So it is apparent that there is a need for an alternative method of obtaining the benefits ink jet technology in the printing of postage meter indicia without losing any of the desirable qualities or characteristics of current methods of indicia printing.